So, why do you write Zaraz wracam, using an imperfective verb "wracać" and not a Perfective one "wrócić"?
For one thing, you can't use a perfective form in the present tense, using the perfective form immediately turns the expression into one in the future tense.
But the interesting question is in the title of your post: "why not?", in other words: when do we use "zaraz wracam
" as opposed to "zaraz wrócę
There's is no difference in meaning, but there is one in usage. Your question has reminded me of the announcement often seen on the doors of small state-owned shops (most of them were such at that time) in Poland in the communist times: "Wyszłam na pocztę. Zaraz wracam.
" Frankly speaking, I would have been surprised if a shop assistant had written: "Wyszłam na pocztę. Zaraz wrócę.
" This announcement was a perfect example of the social code, and its true meaning to any prospective customers was: I am now busy with my own private matters, so I had to go. You may think what you like, but it is pretty unlikely (almost certain!) that I'll be back soon, so please be so kind and go somewhere else
. And that brings us to the real difference in usage (although there is none in meaning): you will typically say "zaraz wrócę" when you refer to a rather immediate future, and the receiver of the information is able to check on the time between your statement and the actual fact expressed in it. The lady in the shop would have never say that as this would sound ridiculous to her customers who knew she might be back in her shop just fifteen minutes before the closing time at 6 o'clock p.m., even if she put her announcement up at the very noon.